FOEEWORD. 



Most of the material used in the study of the approximately 150 

 uew species, subspecies, and formae described were obtained from 

 museum specimens of Anura that had lain long in alcoliol, some for 

 more than 80 3ears. While much of this material was in remarkably 

 good condition, allowing the study even of cytological details, it is 

 readily understood that the material as a whole was far from satis- 

 factory', both because too limited in extent and because not always 

 well preserved. Divergent races are prevalent in many species of 

 Protozoa, and abundant material from different sources should be 

 used in taxonomic studies in this group. Because of the limited ma- 

 terial, often ill preserved, the author regards his results as only ten- 

 tative, constituting a preliminary review of the taxonomy of the 

 Opalinidae and subject to extensive modification through intensive 

 study of more favorable material. 



Similarly, in the chapter devoted to a discussion of the geographic 

 distribution of the Anura and their Opalinid parasites, many of the 

 suggestions are but tentative, pending a more thorough knowledge 

 of geographic conditions in previous geologic periods. This chapter 

 is written more for the sake of emphasizing a method of study of 

 paleogeographic problems, the host-parasite method we may call it, 

 than as a definitive contribution to paleogeographic knowledge. 

 Concurrent evidence from the geographic distribution of both ani- 

 mals and their parasites, or host plants and their parasites, is so much 

 more convincing than evidence from either the hosts or the parasites 

 alone, that the host-parasite method of studying these problems can 

 hardly be overemphasized. This method, rather than the particular 

 suggestions in detail, is the thing to be emphasized in the chapter 

 upon geographic distribution. 



M. M. M. 



